Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.
OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.
One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.
One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)3, which has the following structure:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.
As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.
As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.
As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.
A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.
As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.
As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.
As used herein, the term “capping layer” may refer to a layer of material that is deposited over the top electrode of an OLED (which is typically the cathode for top emission devices). The layer is typically used to enhance the amount of light outcoupled from the OLED. The layer may be made of any suitable material (such as Alq3 and is preferably transparent, semi-transparent, or translucent. The term “total capping layer” may refer to the combination of all of the capping layers disposed over (and optically coupled to) an OLED. For instance, if a first and second capping layer are disposed over an OLED such that they are all optically coupled, the total capping layer of the OLED is the combination of the first and second capping layers. The “total optical thickness” is the optical thickness of the total capping layer.
As used herein, the term “optically coupled” may refer to a configuration in which substantially all of the light that is emitted from, or that propagates through, a surface of a first component also propagates through a substantially parallel surface of a second component. A “component” may include an organic device (e.g. OLED, transparent OLED, or top-emission OLED), a layer of an organic device (such as an organic layer, an emitting layer, etc.), a capping layer (which may be disposed over an organic device), a substrate, and/or an electrode of an organic device. For example, an OLED may be optically coupled to a capping layer if substantially all of the light that is emitted from the OLED in a direction perpendicular to one of its electrodes also propagates through a surface of a capping layer that is substantially parallel to the electrode.
As used herein, the term “deposit” or “depositing” includes any known method of fabricating a layer of an organic device on a first substrate, including VTE, OVJP, OVJD, stamping, ink jet deposition, LITI, LIPS, as well as fabrication (including photolithography) of a layer on a second substrate followed by alignment of the first and second substrates. Stamping (both additive (i.e. cold welding) and subtractive) is described in detail in U.S. Pat. Nos. 6,294,398, 6,895,667 and 7,964,439 each of which is hereby incorporated by reference.
As used herein, a capping layer or other layer may be “common” to a plurality of organic devices if it is disposed over (e.g. covering) a substantial portion of each of the plurality of OLEDs. For instance, if a capping layer is common to a first and a second OLED, but is not common to a third OLED, then the capping layer will be disposed over a substantial portion of both the first and second OLED, but will not be substantially disposed over the third OLED. Similarly, a layer may be referred to as “non-common” between or among a first and second OLED if the layer is disposed over a substantial portion of the first OLED, but no portion of the layer is disposed over a substantial portion of the second OLED, and if the non-common layer is disposed over none or only a trivial amount of the second OLED.
As used herein, the term “blanket layer” may refer to a layer that is common to all of, or substantially all of the OLEDs on a substrate. A blanket layer may be deposited through a mask that prevents material from depositing around the edges of the substrate (for example, in the area required for encapsulation or in areas requiring electrical contact from an external power supply or video signal). However, the deposition of a blanket layer generally does not involve deposition of materials onto the substrate through a mask that defines features on the substrate (such as individual pixels of one particular color), such as an FMM. In most cases, the mask used does not need to be aligned to a degree of precision that exactly matches the deposition holes with sub-pixel size features on the substrate.
As used herein a “patterned mask” or “fine metal mask” (FMM) may refer to masks that may be used to deposit materials onto a substrate. For VTE, usually the organic and metal layers are deposited through a “patterned mask” including blanket and/or common layers. Thus, the opening (i.e. “hole”) in a “patterned mask” is usually large and covers a significant portion of the display or lighting panel area. In contrast, an FMM may be used to deposit features having a pattern resolution smaller than the entire active (light emitting) area of the substrate. Typically, an FMM has one dimension that is of the order of the dimensions of a portion of the sub-pixels (usually of one color) that is disposed on the substrate. An FMM is thereby typically utilized for the deposition of the emissive layer of an organic device, where the differing colors of the display are each deposited separately through an FMM designed to only allow deposition on a portion of the active OLEDs present in the display (e.g. an FMM through which only the red emissive layer is deposited, another FMM through which only the green emissive layer is deposited, etc.).
All masks whether “patterned” (such as those with a large opening for common deposition) or an FMM require some degree of alignment. However the FMM requires a far tighter alignment tolerance (e.g. on the order of the dimension of a portion of the sub-pixels) and thereby usually takes longer to align, which may add significantly to the time and cost of manufacturing. FMMs also typically require more regular maintenance (i.e. replacement or regular cleaning) than large area “patterned” masks, as the smaller “holes” in the FMM (through which material is deposited) can reduce in size as a function of deposition/production time as material is deposited onto them. This can cause problems in the display area as the deposition area of the FMM is reduced beyond its original design. Moreover, a build-up of material on an FMM can also cause issues related to “flaking” (i.e. material falling off the mask into the chamber or getting onto the substrate), which may create yield problems. These issues may not be as significant for a “patterned” large area mask, as the surface area of the mask onto which material can be deposited is far smaller (i.e. there are larger openings for material to be deposited through).
As used herein, the term “optical thickness” may refer to the product of the physical thickness of an isotropic optical element and its refractive index. The “physical thickness” of a capping layer or other layer refers to the length of the layer in a direction that is substantially perpendicular to the surface of the substrate that an OLED is disposed over.
As used herein, the term “optimized” or “optimal” may refer to maximizing the lifetime or efficiency of an OLED, which may result from reducing the loss of efficiency to less than approximately 5%.
More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.